Joseph Verner Reed Jr., a U.N. undersecretary-general, former U.S. ambassador and chief of protocol under President George H.W. Bush, died Sept. 29 at a hospital in Greenwich, Conn. He was 78.

The death was announced by Fraser Seitel, a longtime friend and colleague. He said Mr. Reed was not ill, and the cause of death was not immediately known.

In a statement, U.N. Secretary General Ban Ki-moon called Mr. Reed “a skilled diplomat, a global citizen, an art lover and a dear friend.”

He noted that Mr. Reed had sent an email to several U.N. colleagues Thursday evening about enhancing the United Nations’ appearance.

“He was a champion of the United Nations to his very last breath,” the secretary general said.

Mr. Reed served in the United Nations for 25 years under four secretaries general and traveled the globe as an envoy for the organization. At the time of his death, he was an undersecretary-general and special adviser to Ban.

Mr. Reed was a descendant of Edward Doty, who came to America on the Mayflower. After graduating from Yale University, he became private secretary to the head of the World Bank.

In 1963, he joined Chase Manhattan Bank, where he became a vice president and assistant to the chairman, David Rockefeller.

“As my closest associate for three decades at the Chase Bank, together we traveled the world,” Rockefeller said in a statement. “Joseph was a true ‘character’ in the very best sense of the word. He was a man of elegance, grace, wit, flamboyance and razor sharp intellect, a diplomat’s diplomat.”

In 1981, Mr. Reed was appointed ambassador to Morocco by President Ronald Reagan. When Bush took office as president in January 1989, he chose Mr. Reed to be chief of protocol, which required him to plan and execute programs for foreign leaders visiting the president and to accompany the president on official visits abroad.

Mr. Reed recalled in an interview last November with the Greenwich Sentinel his worst protocol gaffe: forgetting to ensure that Queen Elizabeth II had a step to stand on for her arrival ceremony at the White House in the spring of 1990. The result, he said, was that “all you could see was her hat bobbing up and down behind the microphones.”

It became known as “the Talking Hat” incident, which Mr. Reed called “a nightmare.”

According to the newspaper, it created a bond between Mr. Reed and the diminutive monarch. Years later, when he attended a dinner on the royal yacht Britannia in Cyprus representing the United Nations, Mr. Reed recalled that the queen pointed to him and said, “You should have the Talking Hat on your tombstone.”

His wife of 56 years, the former Marie “Mimi” Maude Byers, died in 2015. Survivors include two daughters, Serena Reed Kusserow of Santa Barbara, Calif., and Electra Reed of Greenwich; a brother; and four grandchildren.